In recent years, attention has been given to a wireless sensor network system configured such that a plurality of sensors each having a wireless communication function are connected to each other so as to form a communication network. That is, the wireless sensor network system is a system in which, unlike a fixedly built network, an ad-hoc network is built autonomously by sensors. Such a wireless sensor network system finds applications in a device monitoring system in a factory or a plant, an operation management system associated with electric power, gas, waterworks, or the like. Related techniques may be found, for example, in Japanese Laid-open Patent Publication No. 2013-055451.
In such a wireless communication network, there is a possibility that unintended radio wave interference may occur, which may result in a reduction in throughput and/or a reduction in communication quality. The radio wave interference may occur due to causes which may be classified into two types: internal causes in a network; and external causes.
The internal causes originate from a communication collision between wireless devices in the network. Examples of such internal causes include interference that occurs when a plurality of wireless devices operating as hidden terminals start communication at the same time, interference caused by reflection of radio waves radiated by wireless devices, and the like. Related descriptions may be found, for example, in Japanese Laid-open Patent Publication No. 2007-295278.
On the other hand, external causes originate from a radio wave output from an electromagnetic wave source located outside a network. Examples include interference to wireless communication in a network by radio waves radiated by an external device in an electrical substation, an electric power transmission/distribution system, an electric power tower, a railroad, a factory, a base station (radio antenna) of a portable telephone system, or the like. In recent years, wireless communication devices have become popular, which accordingly results in a quick increase in communication failures caused by radio wave interference.